A "Green Tool" for Flue Gas Desulfurization: Magnesium Hydroxide
With increasing global attention to environmental protection, industrial flue gases, particularly sulfur dioxide emissions from coal-fired power plants, metallurgy, and chemical industries, have become a key focus of air pollution control. Among the numerous flue gas desulfurization technologies, one process using magnesium hydroxide as its core material is gaining increasing attention and application due to its high efficiency, cost-effectiveness, and environmental friendliness.
Common Materials for Flue Gas Desulfurization
Before delving deeper into magnesium hydroxide, let's first review several commonly used alkaline absorbent materials in flue gas desulfurization:
Limestone/Lime: This is the most traditional and mainstream desulfurization material, primarily composed of calcium carbonate or calcium oxide. While its technology is mature and widely used, it can sometimes cause equipment scaling and clogging, and the quality and marketability of the byproduct gypsum directly impact its economic viability.
Ammonia: Using ammonia as an absorbent offers high desulfurization efficiency and produces a valuable byproduct—ammonium sulfate fertilizer. However, its cost is relatively high, and there is a risk of secondary pollution from ammonia escape.
Sodium hydroxide: Although it has a fast reaction speed and high efficiency, it is expensive and generally only suitable for small-scale applications or those with extremely stringent desulfurization efficiency requirements.
Magnesium hydroxide: As an emerging high-quality desulfurizer, it stands out among the above materials due to its unique advantages.
The Core Principle of Magnesium Hydroxide Desulfurization
Magnesium hydroxide desulfurization is essentially a classic acid-base neutralization reaction. A prepared magnesium hydroxide slurry is sprayed into the absorption tower, where it comes into contact with high-temperature flue gas containing sulfur dioxide.
The core chemical reaction equation is as follows:
1. Dissolution and Ionization:
Magnesium hydroxide first dissolves in water and ionizes to produce hydroxide ions.
Mg(OH)₂ → Mg²⁺ + 2OH⁻
2. Absorption and Neutralization:
Sulfur dioxide in the flue gas dissolves in water to form sulfurous acid, which then undergoes a neutralization reaction with the hydroxide ions.
SO₂ + H₂O → H₂SO₃
H₂SO₃ + 2OH⁻ → SO₃²⁻ + 2H₂O
3. Oxidation and Crystallization:
The resulting magnesium sulfite is oxidized to stable magnesium sulfate by oxygen in the air.
2MgSO₃ + O₂ → 2MgSO₄
The resulting byproduct is hydrated magnesium sulfate, which is non-toxic, harmless, and widely used. It can be directly discharged or recycled as a resource, truly turning waste into treasure.
